New and better nanostructured materials are needed for various applications in diverse industries including biotechnology, diagnostics, energy, and electronics, among others. For example, electronics manufacturers are continually striving to decrease costs and increase functionality of electronic devices and components. One emerging strategy for cost reduction is directly printing electronics onto low-cost plastic films using solution-based inks. The so called Printed Electronics refers to the technologies of manufacturing functional electronic devices using the processes that have been used in the printing industry, such ink-jet printing, gravure printing, screen printing, flexographic printing, off-set printing, etc. in a high through-put and low-cost reel-to-reel (R2R) fashion. One example of the printed electronics is to construct electrical circuits using inkjet printing of patterns of metal nanoparticles to form conductors. This process is discussed in, for example, “Applications of Printing Technology in Organic Electronics and Display Fabrication”, by V. Subramanian, presented at the Half Moon Bay Maskless Lithography Workshop, DARPA/SRC, Half Moon Bay, Calif., Nov. 9-10, 2000.
Nanoparticle material properties can differ from counterpart bulk materials. For example, one of most characteristic feature of nanoparticles is the size-dependent surface melting point depression. (Ph. Buffat et al.; “Size effect on the melting temperature of gold particles” Physical Review A, Volume 13, Number 6, June 1976, pages 2287-2297; A. N. Goldstein et al. “Melting in Semiconductor Nanocrystals” Science, Volume 256, Jun. 5, 2002, pages 1425-1427; and K. K. Nanda et al.; “Liquid-drop model for the size-dependent melting of low-dimensional systems” Physical Review, A 66 (2002), pages 013208-1 thru 013208-8.) This property would enable the melting or sintering of the metal nanoparticles into polycrystalline films with good electric conductivity. An example has been shown by D. Huang, F. Liao, S. Molesa, D. Redinger, and V. Subramanian in “Plastic-Compatible Low Resistance Printable Gold Nanoparticle Conductors for Flexible Electronic” Journal of the Electrochemical Society, Vol 150, p 412-417, 2003. In order to process the nanoparticle inks on plastic substrate, it is necessary to get the particle sintering temperature below the glass transition temperature (Tg) of the substrate materials, generally less than 200° C. As pointed out in the literature above, it requires the nanoparticles having the dimensions less than 10 nm.
A need exists to find better nanoparticle synthetic routes, particularly at very small dimensions and in commercially feasible ways. For example, a need exists to synthesis inorganic nanoparticles with dimensions less than 20 nm, especially those with dimensions less than 10 nm, in liquid media by commercial mass production, due to the difficulties in control the particle nucleation and growth.
US patent publications 2006/0003262 to Yang et al; and 2006/0263725 to Nguyen et al; describe fabrication and applications of nanoparticles with use of dyes. Here, a solution process for nanoparticle synthesis is briefly described but the process is focused by a number of factors important for commercialization including limitations on the general applicability of the process to various metals and materials including, for example, silver and semiconductors, limitations in use of thiol stabilizing agents, avoid formation of undesired sulfides, and limitations in use of phase transfer catalysts. For example, some phase transfer catalysts can be toxic.
A need exists to find better, more efficient, more versatile methods for scale up for mass production of nanoparticles with low cost process.